Brittle material fine particles with internal strain for use in aerosol deposition method

ABSTRACT

A material composed of brittle material fine particles, such as ceramic or metalloid fine particles, for forming a composite structure on a substrate surface. The brittle material is pretreated to achieve a specific size range of fine particles and to develop a desired range of internal strain therein. The brittle material fine particles are adapted to form an aerosol with a gas stream, and when the aerosol is ejected to collide with a substrate surface, this causes collision of brittle material fine particles with a substrate surface thus imparting a mechanical impact to the fine particles. Such mechanical impact fractures or deforms the particles, and thereby generates an active new surface for brittle material fine particles after being fractured or deformed.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is a divisional application of co-pending U.S.patent application Ser. No. 10/070,104, filed on Oct. 3, 2002, which inturn is a 371 (national phase) of PCT International Serial No.PCT/JP00/07076 filed Oct. 12, 2000. The subject matter of these prioritydocuments is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a material composed of brittle materialfine particles, such as ceramic or metalloid fine particles, for forminga composite structure on a substrate surface. More particularly, thepresent invention relates to brittle material fine particles, having adesired range of size and internal strain, which are adapted to form anaerosol with a gas stream, and when the aerosol is ejected to collidewith a substrate surface, the fine particles generate an active newsurface after being fractured or deformed due to mechanical impact.

2. Description of the Prior Art

Generally, when a ceramics sintered body is formed, a liquid phasesintering is carried out in which a sintering assistant is added to makethe inter-jointing of ceramic particles easier so as to form a liquidphase near the boundary face at which the particles join.

Hot pressing is known as a method for forming a high-density sinteredbody without using the sintering assistant. A vapor deposition methodsuch as PVD and CVD or a thermal spraying method is also known as amethod of forming a coat such as a metal or a ceramic on a substratesurface.

On the other hand, a gas deposition method (published in a metalmagazine “KINZOKU” issued in January 1989 by Mr. KASHU, Seiichiro) andan electrostatic fine particle coating method (published in an advanceprinting used in an academic lecture meeting by Mr. Ikawa et al. in thePrecision Machine Society of Japan held in the autumn of 1977) are alsoknown as new coat-forming methods. In the former, it is a basicprinciple that ultra-fine particles such as metal or ceramic are madeinto an aerosol by gas agitation and accelerated through a minutenozzle. When the ultra-fine particles collide with a substrate, a partof their kinetic energy is converted to thermal energy to causesintering between the fine particles or between the fine particles andthe substrate. In the latter, it is a basic principle that fineparticles are charged and accelerated using a gradient of an electricfield, and then sintered in the same manner as in the gas depositionmethod using the thermal energy generated when the fine particlescollide with the substrate.

Further, examples of the prior art which have improved the gasdeposition method or the electrostatic fine particle coating methodstated above are disclosed in Japanese Unexamined Patent Publication No.HEI 8-81774, Japanese Unexamined Patent Publication No. HEI 10-202171,Japanese Unexamined Patent Publication No. HEI 11-21677 or JapaneseUnexamined Patent Publication No. 2000-212766.

In the art disclosed in Japanese Unexamined Patent Publication No. HEI8-81774, two kinds of metal or organic substances with different meltingpoints are heated to evaporation by resistance wire heating, electronbeam heating, high-frequency induction heating, sputtering, arc plasmaor the like to produce ultra-fine particles of 0.1 μm or less of whichthe surface is very active. These ultra-fine particles are sprayed,every metal with a different melting point, on a substrate using anozzle based on sectional CAD data for a three-dimensional shape. Thisoperation is repeated to form a substance with a three-dimensional shapeconsisting of two kinds of metals with different melting points. Thesubstance with a three-dimensional shape is then heated at anintermediate temperature between the melting points of the two kinds ofmetal to melt and remove a metal portion with a low melting point,thereby leaving a metal portion with a high melting point.

In the art disclosed in Japanese Unexamined Patent Publication No. HEI10-212171, the ultra-fine particles obtained by heating and evaporatingthe metal or the organic substance using resistance wire heating,electron beam heating, high-frequency induction heating, sputtering, arcplasma or the like as stated above are sprayed on the substrate throughan opening of a mask. In this manner, a substance of a three-dimensionalshape with no sagging shoulders is formed.

In the art disclosed in Japanese Unexamined Patent Publication No. HEI11-21677, when an aerosol including the above-mentioned ultra-fineparticles is conveyed or the metal or a ceramic is heated andevaporated, a classifying device is provided in an intermediate channelto prevent the ultra-fine particles from cohering together to becomelarger particles.

Referring to the art disclosed in Japanese Unexamined Patent PublicationNo. 2000-212766, when an ion beam, an atomic beam, a molecular beam or alow temperature plasma is irradiated on the ultra-fine particles of 10nm˜5 μm (which are not obtained by heating and evaporation unlike theabove-mentioned prior art), the ultra-fine particles are activatedwithout melting. In such a condition, the activated ultra-fine particlesare sprayed onto the substrate at a speed of 3 m/sec.˜300 m/sec. topromote inter-jointing of the ultra-fine particles thereby forming astructure.

In the liquid phase sintering using a general sintering assistant, aglassy phase including the sintering assistant is formed near a grainboundary. As a result, purity of the ceramics obtained does notincrease, and it is difficult to form a compact body.

On the other hand, it is possible to form ceramics of high purity andcompactness thanks to the atomization of ceramic particles, adoption ofa high sintering temperature, baking under a pressurized environmentsuch as the hot pressing method or the like, removal of the sinteringassistant, etc. However, inclusive of the above, to effect baking is tolet the particles join together by the diffusion of atoms and eventhough the raw powder is minute particles, particle growth is producedduring heating. It is therefore impossible to let a formed subjectremain as minute crystals. Namely, in baking, it is difficult to form apolycrystalline substance consisting of crystal grains of a nanometerlevel.

Further, during baking using a sintering assistant, a specific elementsegregates on a boundary face between the particles, resulting inpreventing the accomplishment of the desired characteristics.

On the other hand, in PVD or CVD, there is a technical characteristicwhereby a structure is formed by accumulation of atoms. Since a crystalplane of which the crystal growth energy is low grows faster, there is acharacteristic structure that the crystal is oriented or the crystal isformed in a columnar shape from the substrate. It is therefore difficultto form a granular polycrystalline substance with disordered crystalorientation.

Referring to thermal spraying, compactness of the formed subject isattained thanks to atomization of the raw powder, processing at hightemperature, environment under reduced pressure or the like. However,there is a technical characteristic whereby a surface layer of the rawpowder is melted to collide with the substrate and let the particlesjoin together. Accordingly, there is a problem that the crystals of theformed subject are shaped by deposition of flat particles in layers ornon-molten particles are mixed into the formed subject. It is alsodifficult to form the polycrystalline substance consisting of crystalgrains in the nanometer level. From the process point of view, there isstill a problem whereby all the techniques above require a hightemperature environment from several hundreds to 10,000° C. and theenergy input is quite large.

Referring further to formation of a ceramic coat by a sol-gel method, atechnique that can form a coat of which the crystallite is comparativelysmall at a low temperature has been developed. However, the coatthickness attained in one coat forming process is generally at a levelfrom several nm to several hundreds nm, and when a thick coat is formed,it is necessary to repeat this process. In this case, it issubstantially necessary to apply a heat treatment to strengthen the coatthat is already applied, wherein particle growth is caused in such acoat layer. There is a problem that the compactness does not increasewhen a coat is formed at a low temperature at which the particle growthis not produced. A problem whereby a crack is produced on the coat whenthe coat forming process is repeated many times has not yet been solved.Further, the ceramics coat forming method for a fine structure such asthe sol-gel method or a deposition method in a solution is a wet processin many cases. Thus, there is some possibility that other solutes orsolvents in the solution are mixed in the coat to generate deteriorationof the coat characteristics or deformation of composition.

In the methods disclosed in Japanese Unexamined Patent Publication No.HEI 8-81774, Japanese Unexamined Patent Publication No. HEI 10-202171,and Japanese Unexamined Patent Publication No. HEI 11 -21677, heatingmeans for obtaining the ultra-fine particles (such as resistance wireheating, electron beam heating, high-frequency induction heating,sputtering or arc plasma) is needed. Further, since the basic principleis that the kinetic energy is converted to thermal energy upon collisionto effect sintering, a particle size of the structure formed on thesubstrate is larger than that of the ultra-fine particles of the rawmaterial due to particle growth.

On the other hand, applicants of the present invention have improved thetechniques disclosed in Japanese Unexamined Patent Publication No.2000-212766. As a result, it became clear that a brittle material suchas a ceramic or a metalloid shows a different behavior from a metal(spreading material).

In the brittle material, it was possible to form a structure withoutirradiating with an ion beam, atomic beam, molecular beam, lowtemperature plasma, etc., in other words, without using any particularactivation means. However, even though fine particles of 10 nm˜5 μm anda collision speed of 3 m/sec.˜300 m/sec. which are the conditionsdescribed in the published specification, are met, there were newproblems in that peel strength of the structure is not enough, partialpeeling can easily occur, or the density is not uniform.

SUMMARY OF THE INVENTION

The present invention was completed based on the following knowledge.

The ceramic is in an atomic bond state in which covalent bonding orionic bonding which does not generally have a free electron is strong.Thus, the ceramic shows strong resistance to hardness, but is weakagainst impact. A metalloid such as silicon or germanium is also abrittle material that does not exhibit spreading.

Accordingly, when a mechanical impact force is applied to these brittlematerials, deformation of a crystal lattice is caused, for example,along a cleavage plane such as a boundary face of crystallites, or thebrittle material is fractured. Once these phenomena are caused, atomsthat initially existed inside and have bonded with other atoms appear inthe deformed surface or the fracture surface. In other words, newsurfaces are formed therein. One atomic layer section of this newlyformed surface is forcibly exposed in an unstable state instead of astable atomic bonding state by external force. Namely, the atomic layersection is placed in a state of high surface energy. This active surfacebonds with the adjacent brittle material surface, the adjacent newlyformed surface of the brittle material, or a substrate surface andbecomes stable. Addition of a continuous external mechanical impactforce continuously generates this phenomenon and as a result of repeateddeformation, fracture or the like of fine particles, development ofbonding and compactness of the structure formed by the development ofbonding are effected. In this manner, the structure of the brittlematerial is formed.

A microscopic construction of the structure made of brittle materialsaccording to the present invention based on the above-mentionedknowledge is obviously different from that of the structure obtained byconventional manufacturing methods.

Namely, a composite structure according to the present invention isprovided in which a structure made of a brittle material such as aceramic or a metalloid is formed on a substrate surface, characterizedin that the structure is polycrystalline, crystals forming the structureare not substantially provided with crystal orientation, a boundarylayer consisting of hyaline does not substantially exist on a boundaryface of the crystals, and part of the structure is an anchor sectionwhich bites into the substrate surface.

Now, the terms important to understand the present invention are definedas follows.

Polycrystal

The term “Polycrystal” means a structure formed by joining andintegrating a crystallite. The crystallite substantially forms a crystalby itself and the size (diameter) thereof is usually 5 nm or more. Thereis some possibility that the fine particles exist in the structurewithout being fractured, but they are substantially polycrystalline.

Crystal Orientation

The term “Crystal Orientation” means an orientation state of a crystalaxis in the structure that is polycrystalline. JCPDS (ASTM) data used asstandard data by an X-ray diffraction of powder which is generallyconsidered to substantially have no orientation is used here as an indexof judgement as to whether there is any orientation in the crystals. Ina viewpoint shown in a twelfth embodiment described below, reference ismade to “substantially no orientation” when the displacement of a majorpeak falls within 30%.

Boundary Face

The term “Boundary Face” means an area where a boundary is formedbetween crystallites.

Boundary Layer

The term “Boundary Layer” means a layer which has a certain thickness(usually several nm˜several μm) in a boundary face or a grain boundarywhich is referred to in a sintered body. The boundary layer usually hasan amorphous structure that is different from a crystal structure withina crystal grain. In some cases, it includes segregation of impurities.

Anchor Section

The term “Anchor Section” means an irregularity formed on the boundarybetween a substrate and a structure. In particular, the irregularity isnot formed on the substrate in advance, but formed by changing surfaceprecision of the original substrate when a structure is formed.

Average Crystallite Size

The term “Average Crystallite Size” means the size of a crystallitecomputed by a method of Scherrer in an X-ray diffraction method. In thepresent invention, the sizes were measured and computed using an MXP-18made by MAC Science Co., Ltd.

Nonstoichiometric Deficiency

The term “Nonstoichiometric Deficiency” means a state in which one ormore kinds of elements are missing from a compound composition ofcrystals forming a structure and as a result, the composition ratio ischanged. The existence of this nonstoichiometric deficiency section canbe checked using an alternative characteristic such as electricresistivity.

Internal Strain

The term “Internal Strain” means a lattice strain included in the fineparticles and is a value calculated using the Hall Method in an X-raydiffraction measurement. A reference material in which the fineparticles are sufficiently annealed is used as a standard and thedisplacement relative to the reference material is shown by apercentage.

Re-Cohesion

The term “Re-cohesion” means a state in which minute fragments fracturedor dropped from the surface of primary particles of the fine particlesduring crushing or milling of the fine particles adhere to and bond withthe surface of the primary particles (which are not necessarily thesame) to form a surface layer.

Referring to a structure consisting of a brittle material formed byconventional sintering, the crystals involve particle growth due to heatand, in particular, when a sintering assistant is used, a hyaline isproduced as a boundary layer.

Further, since the composite structure according to the presentinvention, involves deformation or fracture of the raw fine particles,constitutive particles of the structure are smaller than the raw fineparticles. For example, if the average size of the fine particlesmeasured by a laser diffraction method or a laser scattering method is0.1˜5 μm, the average crystallite size of the structure formed is 100 nmor less in many cases. In this manner, the composite structure has apolycrystalline substance consisting of these fine crystallites as itscomposition. As a result, it is possible to form a compact compositestructure of which the compactness is 70% or more when the averagecrystallite size is 500 nm or less, or the compactness is 95% or morewhen the average crystallite size is 100 nm or less, or the compactnessis 99% or more when the average crystallite size is 50 nm or less.

Now, the compactness (%) can be computed from the following expressionusing the true specific gravity from a bibliographic value or atheoretically calculated value and the bulk specific gravity obtained bythe weight and bulking value of the structure:Compactness=(Bulk specific gravity/true specific gravity)×100 (%)

Further, since the characteristic of the composite structure accordingto the present invention involves deformation or fracture due tomechanical impact such as a collision, it is difficult to get a flat orelongated crystal shape. Accordingly, the crystallite shape issubstantially granular and its aspect ratio is about 2.0 or less.Further, since the composite structure is a section where fragmentaryparticles rejoined after fracture of the fine particles, there is nocrystal orientation. Since the composite structure is almost compact, ithas excellent mechanical and chemical properties such as hardness, wearand abrasion resistance and corrosion resistance.

In the present invention, since the action from fracturing of the rawfine particles to the re-joining thereof is carried out in an instant,diffusion of atoms is seldom effected near the surface of minutefragmentary particles during joining. Accordingly, there is no disorderin the atomic arrangement at the boundary face of crystallites of thestructure. A boundary layer (hyaline) which is a dissolved layer isseldom formed. Even if the boundary layer is formed, the thickness ofthe layer is 1 nm or less. Accordingly, the composite structure showsexcellent characteristics for the chemical properties such as corrosionresistance.

Further, the composite structure according to the present inventionincludes a crystal with a nonstoichiometric deficient section (forexample, deficiency of oxygen) near the boundary face of the crystalsforming the structure.

A substrate forming the composite structure according to the presentinvention includes glass, metal, ceramic, metalloid or an organiccompound. A brittle material includes the following: an oxide such asaluminum oxide, titanium oxide, zinc oxide, tin oxide, iron oxide,zirconium oxide, yttrium oxide, chromium oxide, hafnium oxide, berylliumoxide, magnesium oxide or silicon oxide; carbide such as diamond, boroncarbide, silicon carbide, titanium carbide, zirconium carbide, vanadiumcarbide, niobium carbide, chromium carbide, tungsten carbide, molybdenumcarbide, or tantalum carbide; nitride such as boron nitride, titaniumnitride, aluminum nitride, silicon nitride, niobium nitride, or tantalumnitride; boride such as boron, aluminum boride, silicon boride, titaniumboride, zirconium boride, vanadium boride, niobium boride, tantalumboride, chromium boride, molybdenum boride, or tungsten boride; thecompounds thereof or solid solution of a hypercomplex system;piezo-electric/pyro-electric ceramics such as barium titanate, leadtitanate, lithium titanate, strontium titanate, aluminum titanate, PZTor PLZT; Extremely tough ceramics such as SIALON or cermet; livingorganism adaptable ceramics such as apatite hydroxide or calciumphosphate; metalloid substance such as silicon, germanium or othermetalloid in which various kinds of dope substances such as phosphoruswere added to silicon or germanium; or semiconductor compounds such asgallium arsenide, indium arsenide or cadmium sulfide.

The structure section of the composite structure according to thepresent invention can have a thickness of 50 μm or more. The surface ofthe structure is not smooth microscopically. For example, when anabrasive resistant sliding member coated with an extremely hard ceramicis formed on a metal surface, a smooth surface is required. In thiscase, it is necessary to cut or grind the surface in a later process. Insuch a use, it is desirable that the deposition depth of the ceramicstructure be about 50 μm or more. When surface grinding is performed, itis desirable that the deposition depth be 50 μm or more due to themechanical limits of a grinding machine. In this case, since grinding ofseveral tens μm is performed, a thin coat of 50 μm or less with a smoothsurface is formed.

In some cases, it is desirable that the thickness of the structure be500 μm or more. Objects of the present invention are to form not only aceramic coat which has functions such as high hardness, wear andabrasion resistance, heat resistance, corrosion resistance, chemicalresistance, and electrical insulating properties and which is formed ona substrate such as a metallic material, but also to form a structurewhich can be used alone.

The mechanical strength of the ceramic materials varies, but if thestructure has a thickness of 500 μm or more, it is possible to obtain astrength which is suitable, for example, to use as a ceramic substrateif the material is properly selected.

For example, ultra fine ceramic particles are deposited on a surface ofmetal foil set on a substrate holder to form a compact ceramic structureof which part or all has a thickness of 500 μm or more. After formationof the ceramic structure, if the metal foil section is removed, it ispossible to form a machine component of ceramic materials at roomtemperature.

On the other hand, a composite structure forming method according to thepresent invention comprises the steps of first pre-treating brittlematerial fine particles to impart an internal strain to the brittlematerial fine particles, secondly causing the brittle material fineparticles in which the internal strain has been created to collide witha substrate surface at high speed or applying a mechanical impact forceto the brittle material fine particles containing the internal straintherein deposited on the substrate surface, to deform or fracture thebrittle material fine particles, re-joining the fine particles throughactive new surfaces generated by the deformation or fracture, forming ananchor section made of polycrystalline brittle material of which partbites into the substrate surface at a boundary section between the newsurfaces and the substrate, and further forming a structure made ofpolycrystalline brittle material on the anchor section.

When the internal strain is small, it is hard to deform or fracture thebrittle material fine particles upon collision. On the contrary, whenthe internal strain is large, a large crack is caused because theinternal strain is cancelled. In this case, the brittle material fineparticles fracture and cohere before collision. Even though the coheringsubstance is caused to collide with the substrate, it is hard to formthe new surface. Accordingly, to obtain the composite structureaccording to the present invention, the size and collision speed of thebrittle material fine particles are important, but it is more importantto apply a predetermined range of internal strain to the brittlematerial fine particles as raw materials in advance. A strain grows tilljust before the crack is formed is the most desirable strain, but fineparticles in which the internal strain remains are acceptable eventhough some cracks have been caused therein.

As a technique for colliding the brittle material fine particles at highspeed, there is a method using carrier gas, a method for acceleratingfine particles using electrostatic force, a thermal spraying method, acluster ion beam method, a cold spray method and the like. Among these,the method using carrier gas is usually referred to as a gas depositionmethod. This is the method of forming a structure in which an aerosolincluding fine particles of metal, metalloid or ceramics is ejectedthrough a nozzle and sprayed on the substrate at high speed, wherein, byproviding fine particles on the substrate, a deposited layer such as agreen compact having composition of fine particles is formed. Inparticular, a method for directly forming the structure on the substrateaccording to the present invention is hereinafter referred to as“Ultra-Fine Particles Beam Deposition Method”.

In the composite structure forming method (i.e. ultra-fine particlesbeam deposition method) according to the present invention, it ispreferable to prepare and use in advance brittle material fine-particlesof which the average particle size is 0.1˜5 μm and the internal strainis large. It is also desirable that the speed be in a range between50˜450 m/s, but it is more preferable if the speed falls between 150˜400m/s. These conditions are closely related to whether or not a newlygenerated surface is formed upon collision with the substrate. If theparticle size is less than 0.1 μm, it is hard to cause fracture ordeformation because the size is too small. When the particle size ismore than 5 μm, partial fracture is caused, but a trimming effect of thecoat by etching substantially starts to appear. There is also somepossibility that the fine particles are not fractured, but remain in thedeposition of the green compact of the fine particles. Likewise, whenthe structure is formed in this average particle size, a phenomenon thatthe green compact is mixed in the structure has been observed if thespeed is 50 m/s or less. If the speed is 450 m/s or more, it is knownthat the etching effect is remarkable and the structure formingefficiency deteriorates.

Once a crack is caused in raw particles, the internal strain iscancelled. It is therefore desirable to have no cracks, but even thoughthere are some cracks, it does not affect the structure formingefficiency so much if there is a predetermined internal strain. In otherwords, it is most desirable to use the raw fine particles that havestored an internal strain until just before the crack is produced.

As a result of double-checking the contents disclosed in JapaneseUnexamined Patent Publication No. 2000-212766, the present inventor etal. could not necessarily get a satisfactory result regarding brittlematerials such as ceramics, but there is some possibility that theabove-mentioned conditions were not met.

One of the features of a composite structure forming method according tothe present invention is in that the composite structure can be formedat room temperature or at a comparatively low temperature and thus thematerial with a low melting point such as a resin can be selected as thesubstrate.

However, a heating process can be added to the method according to thepresent invention. The structure forming of the present invention ischaracterized in that heat is seldom generated during deformation orfracture of the fine particles and a compact structure can besufficiently formed at room temperature. Accordingly, formation of thestructure does not necessarily involve heat, but heat may be necessaryfor drying the fine particles, removal of surface adsorbates oractivation of the fine particles, or the substrate or structure formingenvironment may be heated to assist in forming the anchor section, torelax thermal stress between the structure and the substrate withrespect to the use environment of the composite structure, to removeadsorbates from the substrate surface, or to improve the structureforming efficiency. Even in this case, it is not necessary to have atemperature so high that the fine particles or the substrate experiencedissolution, sintering or extreme softening. After the structure made ofpolycrystalline brittle material is formed, it is also possible to heatthe structure at a temperature lower than the melting point of thebrittle material so as to provide structured control of the crystals.

Further, in the composite structure forming method according to thepresent invention, it is desirable to perform the operation underreduced pressure to allow activation of a new surface formed on the rawfine particles and maintain this state for a certain period of time.

When the composite structure forming method according to the presentinvention is performed using the ultra-fine particles beam depositionmethod, it is possible to control the kind and/or partial pressure ofthe carrier gas to control the deficiency of an element of a compoundforming the structure made of the brittle material, to control theconcentration of oxygen in the structure, or to form an oxygendeficiency layer of the oxide near the crystalline boundary face in thestructure, wherein the electric characteristics, mechanicalcharacteristics, chemical characteristics, optical characteristics andmagnetic characteristics of the structure can be controlled.

Namely, when the structure formation is performed using an oxide such asaluminum oxide as the raw fine particles of the ultra-fine particlesbeam deposition method while controlling the oxygen partial pressure ofgas used therein, the fine particles are fractured to form finefragmentary particles. In this case, it is considered that oxygen exitsfrom the surface of the fine fragmentary particles to a vapor phase tocause a deficiency of oxygen at the surface layer. Then, since the finefragmentary particles rejoin, an oxygen deficient layer is formed nearthe boundary face of the crystal grains. The deficient element is notnecessarily the oxygen, but may be nitrogen, boron or carbon. This canalso be attained by omission of the element by distribution of anelement amount between the vapor phase and a solid phase in thenon-equilibrium condition or reaction by controlling the partialpressure of a specific gas.

It is possible to control the volume resistivity value, hardness,corrosion resistance, light transmission properties and the like of theceramic structure by the ultra-fine particles beam deposition methodwhich changes the kind of gas and gas partial pressure stated above.Referring, for example, to the aluminum oxide, when the oxygen gaspartial pressure is decreased, an optically clouded structure can beobtained, while when the oxygen gas partial pressure is increased, atransparent structure can be obtained.

In one embodiment of a composite structure forming apparatus accordingto the present invention, a ceramic structure forming apparatus isprovided, in which an aerosol generated by scattering brittle materialultra-fine particles in the gas is ejected and collides with a substrateat high speed to form a structure of ceramic ultra-fine particles,characterized in that the ceramic structure forming apparatus comprisesan aerosol generator for generating the aerosol, a nozzle for ejectingthe aerosol, and a classifier for classifying the ceramic ultra-fineparticles in the aerosol.

In the present invention, it is important to use raw fine particles withinternal strain. Accordingly, it is desirable to provide a mill forimparting the internal strain, for example, pre-treatment equipment suchas a planetary mill which is a means for imparting a high impact to thefine particles, as a separate body from or as a part of the compositestructure forming apparatus.

The brittle material ultra-fine particles are scattered in the gaswithin the aerosol generator to become an aerosol. The aerosol istransported through a carrier pipe to the classifier in which theaerosol is classified for selection of only particles to be deposited.These fine particles are ejected from the nozzle to the substratethrough the carrier pipe at high speed, wherein the fine particlescollide with the substrate and are deposited therein to form a ceramicstructure. Flow velocity of gas is in a range of subsonic speed tosupersonic speed of hundreds to several hundred meters per second. A gasstream can be formed by pressurization using a gas cylinder or an aircompressor disposed before the equipment, or by depressurization by avacuum pump disposed after the equipment, or by a combination thereof.It is also possible to selectively set the absolute pressure anddifferential pressure within an aerosol-generating chamber and near thesubstrate by adjusting the inner diameter or length of the carrier pipe.

As described above, secondary particles cohering in the aerosol can notform a compact ceramic structure even though they collide with thesubstrate. They can only become a green compact. By means of theclassifier used in the present invention, coarse secondary particlesthat prevent formation of the ceramic structure are removed in advanceto select only primary particles. The structure can be formed withoutbaking by ejecting only those primary particles that can impartsufficient kinetic energy from the nozzle.

Referring to another embodiment of the composite structure formingapparatus according to the present invention, a composite structureforming apparatus is provided, in which an aerosol generated byscattering brittle material ultra-fine particles in the gas is ejectedand collides with a substrate at high speed to form a structure ofbrittle material ultra-fine particles, characterized in that thecomposite structure forming apparatus comprises an aerosol generator forgenerating the aerosol, a nozzle for ejecting the aerosol, and ashredder for shredding cohesion of the brittle material ultra-fineparticles in the aerosol (for shredding the brittle material ultra-fineparticles cohering in the aerosol, or for preventing cohesion of thebrittle material ultra-fine particles in the aerosol).

The brittle material ultra-fine particles are scattered in the gaswithin the aerosol generator to become an aerosol, but most of theaerosol forms coarse secondary particles.

Even though the classifier is provided, when the abundance ratio of thesecondary particles in the aerosol is remarkably larger than that of theprimary particles, the amount of the brittle material ultra-fineparticles in the aerosol ejected from the nozzle is very small relativeto the amount of ceramic ultra-fine particles in the aerosol generatedby the aerosol generator. Accordingly, there is concern that, inpractice, the time for forming the ceramic structure becomes longer orthe amount of gas consumption becomes enormous.

To counteract the low figure for this powder use coefficient, theaerosol generated by the aerosol generator is transported through thecarrier pipe to be introduced to the shredder in which secondaryparticles are shredded into primary particles. The aerosol of theseprimary particles is sufficiently accelerated through the carrier pipeto be ejected from the nozzle. The ejected aerosol collides with thesubstrate to form a compact ceramic structure.

According to a still further embodiment of the present invention, acomposite structure forming apparatus is provided, in which aerosolgenerated by scattering brittle material ultra-fine particles in the gasis ejected and collides with the substrate at high speed to form astructure of brittle material ultra-fine particles, characterized inthat the composite structure forming apparatus comprises an aerosolgenerator for generating the aerosol, a nozzle for ejecting the aerosol,a shredder for shredding cohesion of ceramic ultra-fine particles in theaerosol (or for shredding ceramic ultra-fine particles cohering in theaerosol, or for preventing cohesion of ceramic ultra-fine particles inthe aerosol), and a classifier for classifying the brittle materialultra-fine particles in the aerosol.

The brittle material ultra-fine particles are scattered in the gaswithin the aerosol generator to create an aerosol containing manysecondary particles. The aerosol is then introduced into the shredder tobe shredded into primary particles. However, even in this case, it isdifficult in practice to convert all the secondary particles to primaryparticles, wherein the primary particles including some secondaryparticles are guided to the carrier pipe. If coarse secondary particlesexist, when the ceramic structure is formed, part of the secondaryparticles remains non-compacted inside the ceramic structure, adheres tothe surface of the structure so that this creates a problem that hindersfurther formation of the structure, or removes the structure formed.

By providing the classifier after the shredder, it is possible to removethe secondary particles and to eject from the nozzle only the fineprimary particles involved in the formation of the ceramic structure.

In one embodiment of the composite structure forming apparatus accordingto the present invention, a position control means is provided tocontrol the relative position between the substrate and the nozzle.

The substrate is, for example, disposed on a stage which can control theposition in the vertical (Z), longitudinal and lateral (XY) directionsand at an angle (θ). If the substrate position is moved longitudinallyand laterally during formation of the structure, it is possible to forma section of the structure of which the area is larger than the openingof the nozzle. It is also possible to selectively set the depositionthickness by regulating the amount of ceramic ultra-fine particlesejected from the nozzle and a fixed time or travel speed of thesubstrate. If the position in the vertical direction is controlledfollowing the deposition thickness, it is possible to always make thedistance between the nozzle and the ceramic structure constant.

Further, if the nozzle is secured to the end of an arm flexibly movableby computer control or the like and then the deposition operation isperformed controlling the position in the vertical (Z), longitudinal andlateral (XY) directions and at an angle (θ) while tracing the surface ofan object of a complicate shape having a curved surface and an angle, itis possible to coat an object having a complicated shape with theceramic structure.

According to one embodiment of an aerosol generator of the presentinvention, an aerosol generator is provided, which comprises at leastone of a container for containing brittle material ultra-fine particles,a vibration device for imparting a mechanical vibration action to thecontainer, and an electric field generating device for applying anelectric field, wherein the container is provided with an introductionsection for introducing the gas and a guide section for guiding theaerosol.

The brittle material ultra-fine particles are filled into the containeras powder. The gas introduced from the introduction section blows up thebrittle material ultra-fine particles to generate an aerosol within thecontainer. The aerosol is guided out of the guide section. Theintroduction section is, for example, tubular-shaped and inserted andembedded in the brittle material ultra-fine particles powder to releasegas from the inside of the powder. A mechanical vibration action appliedto the container is not only used to impart the kinetic energy forblowing up the ceramic ultra-fine particles, but also has a function ofnewly providing ambient powder near an opening of the introductionsection and of stably generating the aerosol when the introductionsection is embedded in the brittle material ultra-fine particles. It isalso possible to selectively set the amplitude and vibration speed of avibration device to suitably adjust the amount of ultra-fine particlesthat are blown up.

On the other hand, when an electric field is formed around the brittlematerial ultra-fine particle powder which are filled into the containerof dielectric material and are contact-charged using an electric fieldgenerating device for applying an alternating voltage or an electricfield generating device for generating static electricity by friction,the brittle material ultra-fine particles receive a Coulomb force andfloat from the container wall surface. The floating brittle materialultra-fine particles enter a gas stream introduced from the introductionsection to become an aerosol that is then guided out by the guidesection. By regulating the output of the electric field generatingdevice to adjust the strength of the electric field applied, it ispossible to suitably control the amount of brittle material ultra-fineparticles included in the aerosol. Forcibly setting an electrical chargeof the brittle material ultra-fine particles at the charge of one sideis also an effective means. In this case, it is also possible to performthe charging treatment in advance or to apply the electrical fieldtogether with the charging treatment. For example, if a corona dischargeor radioactive rays such as γ (gamma) rays are applied to the brittlematerial ultra-fine particle powder to add or remove electrons, and dcvoltage is applied while charging the primary particles, it is possibleto float the brittle material ultra-fine particles one after another toform the aerosol and at the same time it is also possible to expectshredding of the secondary particles which have been caused to cohere bythe electrostatic force.

According to one embodiment of a classifier of the present invention,the classifier is a guide section of an aerosol generator. Specifically,the classifier is disposed within the aerosol generator. For example, atubular introduction section is embedded in the powder within thecontainer to blow up the brittle material ultra-fine particles withinthe container using the aerosol generator constructed above in which atubular guide section is disposed at the upper section of the container.When the brittle material ultra-fine particles blown up within thecontainer are scattered in the space of the container, the abundanceratio thereof differs in the height direction according to the weight.Comparatively heavy particles like the secondary particles can not risehigh, but comparatively light particles like the primary particles canbe blown up comparatively high because the influence of gravity on themis small and they are susceptible to the resistance of the gas.Accordingly, by selectively setting the vertical position of the guidesection, it is possible to select only the primary particles that areinvolved in the formation of the ceramic structure. Selected aerosolincluding the primary particles of which the amount has been adjusted isejected from the nozzle through the carrier pipe to be deposited on thesubstrate, thereby forming the compact ceramic structure.

According to another embodiment of the aerosol generator according tothe present invention, the container is provided with a sieve and avibration device for imparting a mechanical vibration action to thecontainer. For example, in this aerosol generator, the sieve is disposedat the upper section of the container and the brittle materialultra-fine particle powder is filled into this sieve. The brittlematerial ultra-fine particles to which mechanical vibration has beenapplied by the vibration device are passed through the openings of thesieve, whereby only the brittle material ultra-fine particles which aresmaller than the diameter of the sieve openings pass by their owngravity. The passed brittle material ultra-fine particles enter the gasstream flowing between the introduction section and the guide sectiondisposed at the lower section of the container and become an aerosol.The aerosol is then guided out of the guide section. By adjusting theopening diameter and opening area of the sieve and by adjusting theamplitude and vibration speed of the vibration device, there is anadvantage that the maximum size and amount of the passed brittlematerial ultra-fine particles can be adjusted to generate and provide astable aerosol. When the aerosol is ejected from the nozzle toward thesubstrate for deposition, the ceramic structure forming apparatusprovided with such an aerosol generator is suitable for moving thesubstrate longitudinally and laterally at a fixed speed to obtain aceramic structure with a fixed deposition thickness.

According to one embodiment of a shredder according to the presentinvention, the shredder is provided with an introduction section and aguide section for introducing and guiding the aerosol respectively, andan impact plate against which the aerosol collides, wherein the aerosolcollides with the impact plate at a lower speed than that for forming astructure of the ceramic ultra-fine particles, to shred the ultra-fineparticles which are in a coarse, cohering condition. As described above,the brittle material ultra-fine particles exist as secondary particlesof almost cohering particles, but the aerosol, containing the secondaryparticles generated by the aerosol generator, is introduced as ajet-shaped aerosol stream accelerated by the introduction section of theshredder to collide with the impact plate provided on the downstreamside. The speed of the brittle material ultra-fine particles in theaerosol stream at this time is preferably 200 m or less per second. Thecolliding secondary particles are shredded upon impact to become minuteparticles (i.e. primary particles) which again enter the gas streamafter reflecting and, as a result, they are converted to an aerosolcontaining many primary particles. This aerosol containing many primaryparticles is suitable for forming a compact ceramic structure.

If the angle of the impact plate is set at 30˜60 degrees relative to thetravel direction of the aerosol stream introduced, the direction of thereflection of particles can be easily and suitably set. In particular,when the direction of reflection is set in the opposite direction to agravity vector, it is possible to control movement of the brittlematerial ultra-fine particles in the space after reflection byselectively setting the speed of the colliding brittle materialultra-fine particles and the pressure within the shredder. For example,if the guide section is provided at a higher location than the impactplate, it is easy to apply a classification action to the shredder byusing the height of travel.

In the composite structure forming apparatus according to the presentinvention, it is possible to selectively control the pressure within theapparatus from a vacuum to a range of more than atmospheric pressureusing a gas cylinder or an air compressor disposed on the upstream sideand a vacuum pump disposed on the downstream side. For example, if thepressure within the shredder is controlled in a range from 100 Pa toatmospheric pressure, it is possible to precisely set the direction ofreflection of the brittle material ultra-fine particles and to expectimprovement in the use efficiency of the fine particles and compactnessof the shredder. If the pressure within the shredder is controlled atmore than atmospheric pressure, the brittle material ultra-fineparticles are susceptible to the resistance of the gas and it ispossible to expect improvement in the classification effect.

According to another embodiment of the shredder according to the presentinvention, the shredder is provided with a plurality of introductionsections, wherein a plurality of aerosol streams ejected from theseintroduction sections is caused to collide with one another forshredding.

The aerosol including the secondary particles generated by the aerosolgenerator is introduced as a jet-shaped aerosol stream accelerated bythe plurality of introduction sections of the shredder, wherein theseaerosol streams collide with one another to impart an impact to thesecondary particles included for shredding. In this manner, the aerosolincluding the secondary particles is converted to an aerosol containingmany primary particles. The aerosol including many primary particles issuitable for forming a compact ceramic structure.

According to a still further embodiment of the shredder according to thepresent invention, the shredder is arranged to irradiate the aerosolwith ultrasonic waves and/or microwaves. For example, an ultrasonic waveirradiation section is disposed in the middle of a tubular carrier pipethat communicates from the aerosol generator to the nozzle to irradiatethe aerosol containing many secondary particles with the ultrasonicwaves. The ultrasonic waves are electrically generated by apiezoelectric resonator and amplified using an ultrasonic wave horn thatis a resonator, wherein the ultrasonic waves are transmitted to theultrasonic wave irradiation section and irradiate the aerosol. Thesecondary particles in the aerosol are shredded by the mechanicalmicro-vibration of the ultrasonic wave and converted to primaryparticles. The aerosol including many primary particles is suitable forforming a compact ceramic structure.

On the other hand, one of the factors by which the brittle materialultra-fine particles cohere to form coarse secondary particles iscohesion of the particles by water. Accordingly, if a microwavegenerator is disposed in the middle of the carrier pipe to generatemicrowaves of which the vibration frequency used in high-frequencydielectric heating of water is 2450 MHz or so to irradiate the aerosol,water in the secondary particles is heated and constantly evaporated. Inthis manner, it is possible to remove the factor of cohesion andshredding of the secondary particles to form primary particles can beattained. The aerosol containing many primary particles is suitable forforming a compact ceramic structure.

The shredders described above can be combined to increase the effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a view explaining a first embodiment of a composite structureforming apparatus;

FIG. 2 is a schematic cross-sectional view of an aerosol generator ofthe composite structure forming apparatus;

FIG. 3 is a view explaining a second embodiment of a composite structureforming apparatus;

FIG. 4 is a schematic cross-sectional view of an aerosol generator ofthe composite structure forming apparatus according to the secondembodiment;

FIG. 5 is a schematic cross-sectional view of a shredder of thecomposite structure forming apparatus according to the secondembodiment;

FIG. 6 is a view explaining a third embodiment of a composite structureforming apparatus;

FIG. 7 is a schematic cross-sectional view of an aerosol generatoraccording to a fourth embodiment;

FIG. 8 is a schematic cross-sectional view of a shredder according to afifth embodiment;

FIG. 9 is a schematic cross-sectional view of a shredder according to asixth embodiment;

FIG. 10 is a schematic cross-sectional view of a shredder according to aseventh embodiment;

FIG. 11 is a TEM image of a titanic acid lead zirconate (PZT) structure;

FIG. 12 is a TEM image of raw particles of the PZT;

FIG. 13 is a distribution chart of crystallite size in a structuremeasured from the TEM image;

FIG. 14 is a SEM image of a silicon oxide substrate before the titanicacid lead zirconate (PZT) structure is formed;

FIG. 15 is a TEM image of a boundary section between the titanic acidlead zirconate (PZT) structure and the silicon oxide substrate after thetitanic acid lead zirconate (PZT) is formed;

FIG. 16 is a TEM image of an aluminum oxide structure formed on a glass;

FIG. 17 is a graph showing the relationship between an internal strainand coat thickness of raw fine particles;

FIG. 18 is a SEM image of fine particles corresponding to the point A ofFIG. 17;

FIG. 19 is a SEM image of fine particles corresponding to the point B ofFIG. 17; and

FIG. 20 is a SEM image of fine particles corresponding to the point C ofFIG. 17.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments of the present invention will now be describedwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a view showing a first embodiment of a composite structureforming apparatus. A helium gas cylinder 11 is connected to an aerosolgenerator 13 through a carrier pipe 12 and a nozzle 15 with arectangular opening of 5 mm×0.5 mm is disposed within astructure-forming chamber 14 through the carrier pipe. A tabularsubstrate 16 made of metal aluminum (Al) is mounted facing the nozzle ona substrate holder 17 which is controllable by a computer vertically (Z)and longitudinally and laterally (XY) 10 mm from the nozzle 15. Thestructure-forming chamber 14 is connected to an exhaust pump 18.

In the present invention, since raw fine particles with internal strainare used, a planetary grinder or a mill serving as pre-treatmentequipment for imparting the internal strain to the raw fine particles isarranged next to the aerosol generator 13 or the like. However, it isalso possible to convey the raw fine particles that have beenpre-treated in a different location to be used here.

FIG. 2 is a schematic cross-sectional view of the aerosol generator 13used in the first embodiment. The aerosol generator 13 is provided witha container 131 which stores a ceramic ultra-fine particle powder 132 ofaluminum oxide (Al₂O₃) of which the average primary particle size is 0.5μm. Adsorbed water on the ceramic ultra-fine particle powder has beensufficiently removed in advance by vacuum drying. An introductionsection 133 connected to the carrier pipe 12 not shown in FIG. 2 isembedded in the ceramic ultra-fine particle powder 132. A guide section134 that can slide vertically is disposed at the upper section of thecontainer 131 and connected to the carrier pipe 12 not shown in FIG. 2.A vibrator 135 imparting a mechanical vibration action is connected tothe container 131. An arrow in the figure shows the direction in whichgas and aerosol 136 flow.

Operation of the above ceramic structure forming apparatus will now bedescribed. A gas cylinder 11 is opened so that gaseous helium isintroduced from the introduction section 133 of the aerosol generator 13through the carrier pipe 12 at a flow rate of 2.5 liter/minute. As aresult, the ceramic ultra-fine particle powder 132 with the internalstrain is blown up within the container 132 to generate the aerosol 136.In this case, since the ceramic ultra-fine particle powder 132 iscontinuously supplied near an opening of the introduction section 133 bythe mechanical vibration action of the vibrator 135, the aerosol 136 canbe stably generated. The ceramic ultra-fine particles in the aerosol 136which have cohered to form secondary particles can not move upward toany great extent because they are comparatively heavy. On the contrary,primary particles of low weight or comparatively small particles closeto the primary particles can move upward to the upper part of thecontainer. Accordingly, if the guide section 134 is selectively set toslide so that its position in the vertical direction can be changed, itserves as a classifier which can select ceramic ultra-fine particles ofthe desired particle size and guide them out of the container 131. Theguided aerosol 136 is ejected from the nozzle 15 through the carrierpipe 12 toward the substrate 16 at high speed. The ejection speed of theaerosol 136 is controlled by the shape of the nozzle 15, the length andinner diameter of the carrier pipe 12, the pressure in the gas cylinder11, the cylinder capacity of the exhaust pump 18 or the like. With thesecontrols, for example, if the internal pressure of the aerosol generator13 is set at several tens of thousands Pa and the internal pressure ofthe structure forming chamber 14 is set at several hundred Pa to providedifferential pressure, the ejection speed can be accelerated fromsubsonic to a supersonic range. The ceramic ultra-fine particles in theaerosol 136 which have been sufficiently accelerated to build up kineticenergy collide with the substrate 16 and are fractured into pieces bythe impact energy, whereby these minute fragmentary particles adhere tothe substrate or join together to form a compact ceramic structure. Thesubstrate 16 is provided with a reciprocating motion of 5 mmlongitudinally by the substrate holder 17 during the structure formingoperation, for 10 minutes. With this control, it is possible to form aceramic structure of aluminum oxide of which the deposition thickness isabout 50 μm. Further, if the structure forming time is extended, it ispossible to increase the deposition thickness in proportion to the timeelapsed. Since this ceramic structure has almost the same hardness as abaked body, it is not necessary to further bake it by an additionalheating operation or the like.

Second Embodiment

FIG. 3 is a view showing a second embodiment of a composite structureforming apparatus. In a composite structure forming apparatus 20, an aircompressor 21 for providing compressed air is connected to an aerosolgenerator 23 through a carrier pipe 22. Provided on the downstream sideof the aerosol generator 23 is a shredder 24 which is connected to anozzle 25 with a rectangular opening of 10 mm×0.5 mm. Under atmosphericpressure, a substrate 27 of metal aluminum (Al) is mounted facing thenozzle 25 on a substrate holder 26 which is movable vertically (Z) andlongitudinally and laterally (XY) at intervals of 2 mm from the end ofthe nozzle 25.

FIG. 4 is a schematic cross-sectional view of the aerosol generator 23used in the second embodiment. An introduction section 232 connected tothe carrier pipe 22 not shown in FIG. 4 is disposed on a level with aguide section 233 connected to the carrier pipe 22, not shown in thefigure, relative to a container 231. Provided above the introductionsection 232 and the guide section 233 is a sieve 235 with an openingdiameter of 100 μm into which is disposed a ceramic ultra-fine particlepowder 234 of aluminum oxide (Al₂O₃) of which the average primaryparticle size is 0.5 μm and of which the adsorbed water has beensufficiently removed in advance by vacuum drying. The container 231 isconnected to a vibrator 236 which is adapted to impart a mechanicalvibration action thereto.

FIG. 5 is a schematic cross-sectional view of the shredder 24 used inthe second embodiment. A tubular introduction section 242 connected tothe carrier pipe 22 not shown in FIG. 5 is disposed at the lower sectionof a container 241 and an impact plate 243 is disposed on the downstreamside of the introduction section 242 at an angle of 45 degrees relativeto the introduction direction of the aerosol. Disposed above the impactplate 243 is a vertically slidable guide section 244 connected to thecarrier pipe 22 not shown in FIG. 5. An arrow in the figure shows thedirection in which the aerosol 245 flows.

Operation of the above ceramic structure forming apparatus 20 will nowbe described. The air compressor 21 is activated to compress air. Thecompressed air is introduced from the introduction section 232 of theaerosol generator 23 through the carrier pipe 22 at a flow rate of 15liters/minute. A gas stream is formed between the introduction section232 and the guide section 233 disposed on the downstream side of theintroduction section 232 in parallel therewith. The container 231 iscaused to vibrate by the vibrator 236 to pass the ceramic ultra-fineparticles of a size of 100 μm or less through a sieve 235 in which theceramic ultra-fine particle powder 234 has been accommodated. Theceramic ultra-fine particles enter the gas stream to become an aerosol237 containing many secondary particles. The aerosol 237 is thenintroduced into the shredder 24 through the carrier pipe 22. Since theintroduction section 242 of the shredder 24 is provided with a reducedopening, the aerosol 237 collides with the impact plate 243 under jetconditions, wherein the secondary particles included in the aerosol 237are fractured to primary particles or particles of a size close to thatof the primary particles and reflected as the aerosol 245 and blown tothe upper section of the container 241. If the guide section 244 is slidto selectively set the position in the vertical direction, it can serveas the classifier for selecting and guiding the ceramic ultra-fineparticles with the desired size.

The aerosol 245 containing many primary particles guided out of theshredder 24 is ejected toward the substrate 27 from the nozzle 25 athigh speed. The ejection speed of the aerosol is controlled in a rangefrom subsonic to supersonic by the amount of gas flow from the aircompressor 21. The ceramic ultra-fine particles in the aerosol whichhave been accelerated to develop sufficient kinetic energy collide withthe substrate 27 and are fractured into pieces by the energy of impact.These minute fragmentary particles adhere to the substrate or jointogether to form the compact ceramic structure of aluminum oxide.Deposition thickness of the ceramic structure formed by the operationdescribed above is about 0.5 μm/minute and it increases in proportion totime elapsed. Further, if the substrate holder 26 is selectivelyactivated to move the substrate 27, the desired shaped ceramic structurecan be formed.

Third Embodiment

FIG. 6 is a view showing a third embodiment of a composite structureforming apparatus. A nozzle 31 of the composite structure formingapparatus 30 is connected to an aerosol generator not shown in thefigure through a carrier pipe 32 made of a flexible material. The nozzle31 is held by an end of a flexibly movable arm 34 which is controlled bya computer 33 to face a complicatedly shaped object 35 such as asubstrate.

Operation of the above ceramic structure forming apparatus 30 will nowbe described. The ceramic ultra-fine particles are conveyed from anaerosol generator not shown in the figure through the carrier pipe 32and ejected onto the surface of the complicatedly shaped object 35 fromthe nozzle 31 at high speed for deposition. The movable arm 34 iscontrolled by the computer 33 to trace the surface, i.e., a profile, ofthe complicatedly shaped object 35 to be coated by the ceramic structuremoving at a fixed distance from the surface of the object. In thismanner, the ceramic structure of a uniform deposition thickness iscoated on the surface of the complicatedly shaped object.

Fourth Embodiment

FIG. 7 is a schematic cross-sectional view of an aerosol generator 40according to a fourth embodiment used in a composite structure formingapparatus. An introduction section 42 and a guide section 43 connectedto a carrier pipe not shown in the figure are secured to a container 41made of Teflon material. A plurality of torus electrodes 44 serving aselectric field generating device is disposed around the container 41leaving a space therebetween. The electrodes 44 are connected to an ACpower supply 46 through lead wires 45. Accommodated within the container41 is a ceramic ultra-fine particle powder 47 of aluminum oxide (Al₂O₃).An arrow in the figure shows the direction in which gas and aerosolflow.

Operation of the above aerosol generator 40 will now be described. Inthe case of aluminum oxide or the like with high electrical resistance,the ultra-fine particles are charged bipolarly in many cases by mutualcontact-charging of particles under natural conditions. If the AC powersource 46 is switched ON to apply alternating voltage between theelectrodes 44 and to generate a strong electric field around the powder,the ceramic ultra-fine particle powder 47 receives a Coulomb forceaccording to its charge and the particles float in the container 41. Inthis condition, if gas is introduced from the introduction section 42through the carrier pipe not shown in the figure, the ceramic ultra-fineparticle powder 47 becomes an aerosol 48 which is then guided out of theguide section 43. By selectively setting the field intensity generatedin the container 41, it is possible to control the amount of floatingceramic ultra-fine particles. Accordingly, it is easy to set the aerosol48 at the desired concentration.

Fifth Embodiment

FIG. 8 is a schematic cross-sectional view of a shredder 50 according toa fifth embodiment used in a composite structure forming apparatus. Anintroduction section 52 and an introduction section 53 connected to acarrier pipe, not shown in the figure, are disposed at the lower sectionof a container 51 to allow the extension of the lines from theintroduction sections 52, 53 in the introduction direction of the commonaerosol to intersect. A vertically slidable guide section 54 is disposedat the upper section of the container 51 and connected to the carrierpipe not shown in the figure. An arrow in the figure shows the directionin which the aerosol flows.

Operation of the above shredder 50 will now be described. The aerosol 55conveyed from the carrier pipe is first divided by the introductionsections 52 and 53 and introduced into the container 51 in a jetcondition for collision. In this case, secondary particles of theceramic ultra-fine particles collide with one another and are fractured.They are then converted to primary particles or particles of which thesize is close to that of primary particles. After this, the aerosol 55is blown up within the container 51. If the guide section 54 is slid toselectively set the position in the vertical direction, it serves as aclassifier that can select and guide the ceramic ultra-fine particles ofthe desired size.

Sixth Embodiment

FIG. 9 is a schematic cross-sectional view of a shredder 60 according toa sixth embodiment used in a composite structure forming apparatus. Atubular ultrasonic irradiation section 61 is disposed in the middle of acarrier pipe 62 and connected to a piezoelectric vibrator 64 through anultrasonic horn 63. The piezoelectric vibrator 64 is connected to anultrasonic oscillator 66 through lead wires 65. The ultrasonicoscillator 66 is then connected to a power supply not shown in thefigure. An arrow in the figure shows the direction in which the aerosolflows.

Operation of the above shredder 60 will be described hereunder. Theultrasonic oscillator 66 oscillates the piezoelectric vibrator 64 togenerate high frequency ultrasonic waves. The high frequency ultrasonicwaves are amplified by the ultrasonic wave horn 63 and propagated to theultrasonic wave irradiation section 61, wherein the high frequencyultrasonic waves converge toward the center of a tube and are applied ata high acoustic pressure. The aerosol 67 is introduced through thecarrier pipe 62 to the ultrasonic wave irradiation section 61, whereinsecondary particles contained in the aerosol are subjected tomicro-vibration by high frequency ultrasonic waves and fractured intoprimary particles or particles of a size close to that of primaryparticles. Since the ultrasonic wave in the air can be propagated easierwithout appreciably damping the acoustic pressure level if the gaspressure is higher, it is desirable to set the gas pressure of theaerosol 67 at more than atmospheric pressure to improve the shreddingefficiency.

Seventh Embodiment

FIG. 10 is a schematic cross-sectional view of a shredder 70 accordingto a seventh embodiment used in a composite structure forming apparatus.A tubular microwave irradiation section 71 is disposed in the middle ofa carrier pipe 72. A microwave oscillator 73 is disposed to surround themicrowave irradiation section 71 and is connected to a power source 75through lead wires 74.

Operation of the above shredder 70 will now be described. When the powersource 75 is switched ON, the microwave oscillator 73 oscillates to formmicrowaves of a frequency of 2450 MHz. An aerosol 76 is introduced bythe carrier pipe 72 to the microwave irradiation section 71 where themicrowaves are applied. Water which is included in the secondaryparticles contained in the aerosol 76 and is a polar molecule which is aprimary factor causing cohesion is heated by a dielectric loss of themicrowave irradiation and instantaneously evaporates. Accordingly, theprimary particles desorb and are fractured.

Eighth Embodiment

FIG. 11 is a TEM image of a titanic acid lead zirconate (PZT) structureformed on a silicon oxide substrate using an ultra-fine particles beamdeposition method among composite structure forming methods according tothe present invention. FIG. 12 is a TEM image of raw particles of PZTused in the ultra-fine particles beam deposition method and FIG. 13 is adistribution chart showing crystallite size in the structure measuredfrom the TEM image.

Internal strain of the raw particles was about 1 % and the size of theraw particles was several hundreds nm. On the other hand, thecrystallite size of the structure obtained from the figure is almost 40nm or less and it was observed that these crystallites join togetherwithout leaving a space therebetween. It is not recognized that there isany crystal orientation, and there is no hyaline on a grain boundary ofthe crystals.

FIG. 14 is a SEM image which shows the surface roughness of the siliconoxide substrate before the titanic acid lead zirconate (PZT) structureis formed. FIG. 15 shows a TEM image at a boundary section between thetitanic acid lead zirconate (PZT) structure and the silicon oxidesubstrate after the titanic acid lead zirconate (PZT) is formed. Bycomparing the two figures, FIG. 14 and FIG. 15, it is seen that a partof the titanic acid lead zirconate (PZT) structure bites into thesilicon oxide substrate to form an anchor section.

The Vickers hardness of this structure is 300˜500 kg f/mm². This meansthat the structure is provided with almost the same mechanicalproperties as a baked body.

Ninth Embodiment

FIG. 16 shows a TEM image of an aluminum oxide structure of a cubiccontent of 2×10^(−9 m) ³ formed on glass using the ultra-fine particlebeam deposition method described above. FIG. 17 is a graph showing therelationship between an internal strain and coat thickness of raw fineparticles.

The internal strain of the raw particles is about 1% and the sizethereof is about 400 nm. It has also been observed that the size ofcrystallite forming the raw particles is 24 nm using the Scherrer & HallMethod which is an X-ray Diffraction Measuring Method (measuringinstrument is an MXP-18 made by MAC Science Co., Ltd.). On the otherhand, the crystallite size of the structure was 9.8 nm using the X-rayDiffraction Measuring Method. It is clear that the structure is apolycrystalline substance made of crystallites minuter than the rawparticles.

A boundary layer (hyaline) in which the atomic arrangement is random cannot be observed on the boundary face between crystallites from FIG. 16and it is clear that the crystallites join together directly. It isobserved that these crystallites are granular in which the aspect ratiodoes not exceed 2 to any great extent. The orientation of the crystal israndom and compact.

This structure exhibits a Vickers hardness of 1000 kg f/mm² or more andhas almost the same mechanical properties as a baked body.

Tenth Embodiment

The raw fine particles used in the eighth and ninth embodiments werepretreated to form the internal strain therein. On the other hand, whenthe raw fine particles without internal strain are used, desired resultswere not attained.

Experiments regarding the relationship between the internal strain andcoat thickness have been made and the results are shown in FIG. 17.Milling was carried out on the aluminum oxide fine particles of whichthe purity is 99.6% using a planetary mill. After changing thecharacterization of the fine particles, a structure was formed on thealuminum substrate using the Ultra-Fine Particles Beam DepositionMethod. The internal strain of the ultra-fine particles was measured byX-ray diffraction. Heat aging was applied to the fine particles toremove the internal strain therefrom. The condition in which theinternal strain was removed was set as 0% of a strain amount to be usedas a reference strain amount.

SEM photos (taken using Hitachi made In-lens SEM S-5000) of fineparticles at the points A, B and C in FIG. 17 are shown in FIGS. 18, 19and 20 respectively.

It is clear from FIG. 17 that an internal strain of 0.25%˜2.0% isdesirable. Referring to the relationship between a crack and theinternal strain, if there is no internal strain, no crack is generatedas shown in FIG. 18. However, If an internal strain greater than a fixedvalue (in the present invention, an internal strain more than 2.0%) isfound, the crack has been completely formed and the fragments droppingfrom the crack adhere to the surface to form such a re-cohered conditionas shown in FIG. 20.

As described above, in the milling treatment for imparting strain to thefine particles, it is desirable to use a milling means that can impart alarge impact for milling the fine particles. This is because acomparatively equal and large strain can be imparted to the fineparticles. As such a milling means, it is desirable to use a vibratingmill, attriter or planetary mill which can impart larger gravitationalacceleration compared with a ball mill which is often used in themilling treatment of ceramics. In particular, it is most desirable touse a planetary mill that can impart an especially large gravitationalacceleration rather than a ball mill. Referring to the condition of thefine particles, since the crack cancels the internal strain, it is mostdesirable to use fine particles in which the internal strain hasincreased until just before a crack is caused. FIG. 19 shows thecondition in which some cracks are caused, but sufficient internalstrain is still left.

As described above, in the composite structure according to the presentinvention, a composite structure is provided, in which a structure madeof a brittle material such as a ceramic or metalloid is formed on asubstrate surface, wherein the structure is polycrystalline and crystalsforming the structure do not substantially exhibit crystal orientation,while a boundary layer made of hyaline does not exist on a boundarylayer between crystals, and part of the structure is an anchor sectionbiting into the substrate surface. Accordingly, the composite structureexcels in joint strength with the substrate. Compactness of thestructure itself is high and the size of constituent particles isuniform and extremely small. Accordingly, mechanical, electrical andchemical properties that were not available in the prior art can beexpected.

Further, if the method of forming a composite structure according to thepresent invention is used, it is possible to form a high density andhighly compact composite structure without baking.

Using the ceramic structure forming method according to the presentinvention, if the aerosol of ceramic ultra-fine particles is stablygenerated and the secondary particles in the aerosol are shredded beforedeposition, a compact ceramic structure can be suitably formed. Eventhough the substrate or nozzle is caused to move at a fixed speed, it ispossible to maintain a fixed deposition thickness.

Eleventh Embodiment

This embodiment refers to a nonstoichiometric deficiency.

First, using aluminum oxide fine particles of 99.8% purity, an aluminumoxide thin coat ceramic structure of 8 μm thickness was formed on abrass substrate using the Ultra-Fine Particles Beam Deposition Method ofthe present invention in which the kind of gas and gas pressure in theaerosol have been changed. A measured value of electric resistivity(volume resistivity value) of this structure is shown below:

-   A: When nitrogen is 100%: Volume resistivity value=4.2×10¹⁰ Ω·cm-   B: When nitrogen is 50% and oxygen is 50%: Volume resistivity    value=2.0×10¹⁴ Ω·cm

The volume resistivity of the aluminum oxide according to the literatureis 10^(14˜15) Ω·cm. It is generally known that electronic conductivityand ionic conductivity are generated by deficiency of oxygen in thealuminum oxide to provide a solid electrolyte of which the resistancevalue decreases. In this case, the volume resistivity value of a purealuminum oxide can be used as an alternative characteristic.

Twelfth Embodiment

This embodiment refers to crystal orientation.

Using aluminum oxide fine particles of an average size of 0.4 μm, analuminum oxide structure with the thickness of 20 μm was formed on astainless substrate by the ultra-fine particles beam deposition methodof the present invention. The crystal orientation of this structure wasmeasured by the X-ray diffraction method (MXP-18 made by MAC ScienceCo., Ltd.). The measured results are shown in Table 1.

In Table 1, results of an integrated intensity calculation of four peakpoints of a typical face shape are shown by an intensity ratio where{hk1}={113} is 100. From the left, results where raw fine particles weremeasured by a thin coat optical system, results where the structure wasmeasured by a thin coat optical system, JCPDS card 74-1081 corundumaluminum oxide data, and results where raw fine particles were measuredby an integrated optical system are described respectively.

Since the results for the raw fine particles by the integrated opticalsystem are almost the same as those for the raw fine particles by thethin coat optical system, the results for the raw powder by the thincoat optical system are set as a standard in a non-orientationcondition. The deviation of the intensity ratio of the structure isshown as a percentage (see Table 2). When {113} is set as the standard,displacement of the remaining three peaks falls within 11% and it can besaid that the structure substantially has no crystal orientation. TABLE1 Raw fine Raw fine particles Structure particles (Thin coat (Thin coatCard (Integrated hkl optical system) optical system) 74-1081 opticalsystem) 110 72.0 64.2 579 69.5 121 100 100 999 100 120 77.0 73.4 86677.0 132 69.9 64.2 680 66.0

TABLE 2 hkl Displacement of orientation 110 10.8%  121   0% 120 4.7% 1328.2%

A composite structure according to the present invention is provided inwhich a ceramics structure of a predetermined thickness can beintegrally formed on various substrates. Accordingly, the compositestructure can be utilized in the following:

Minute mechanical parts, abrasion proof coat of magnetic heads,electrostatic chucks, sliding members, abrasion proof coating such asmetal dies and repairing of worn sections and deficient sections,insulation coating of electrostatic motors, artificial bones, artificialroots of a tooth, condensers, electronic circuit parts, oxygen sensors,oxygen pumps, sliding sections of valve, strain gauges, pressuresensitive sensors, piezoelectric actuators, piezoelectric transformers,piezoelectric buzzers, piezoelectric filters, optical shutters,knock-sensors of motor vehicle, ultrasonic wave sensors, infrared raysensors, vibration proof plates, tools for cutting work, surface coatingof a drum for a copying machine, polycrystalline solar batteries,pigment sensitizing type solar batteries, surface coating of kitchen andother knives, balls of ball-point pens, temperature sensors, insulationcoating of displays, superconductor coatings, Josephson junctiondevices, superplastic structural bodies, ceramic heaters, microwavedielectric substances, water repellent coatings, antireflectioncoatings, heat reflecting coatings, UV absorbent coatings, IMD (layerinsulation coatings), shallow trench isolation (STI) or the like.

Although there have been described in detail what are the illustrativeembodiments of the present invention, it will be understood by personsskilled in the art that variations and modifications may be made theretowithout departing from the gist, spirit or essence of the invention. Thescope of the invention is indicated by the appended claims.

1. Brittle material fine particles for forming a structure on asubstrate surface, wherein the particles deform or fracture uponcollision with a substrate or when a mechanical impact is impartedthereto, and the particles are provided with internal strain such thatthe particles generate an active new surface after being fractured ordeformed.
 2. The brittle material fine particles according to claim 1,wherein the internal strain of the fine particles is 0.25%˜2.0%.
 3. Thebrittle material fine particles according to claim 1, wherein an averagesize of the fine particles is 0.1˜5 μm.
 4. The brittle material fineparticles according to claim 2, wherein an average size of the fineparticles is 0.1˜5 μm.
 5. The brittle material fine particles accordingto claim 1, wherein the fine particles are adapted to be incorporatedinto an aerosol so that the mechanical impact can be imparted thereto byblowing the aerosol against the substrate.
 6. The brittle material fineparticles according to claim 1, wherein the internal strain is a latticestrain in the fine particles.
 7. The brittle material fine particlesaccording claim 1, wherein the brittle material fine particles areprovided with an increased said internal strain by processing thebrittle material particles in at least one of a planetary grinder and amill.
 8. The brittle material fine particles according to claim 2,wherein a value of the internal strain is calculated using Scherrer &Hall Method of an X-ray diffraction measurement.
 9. A brittle materialfor forming composite structure on a substrate surface, said materialcomprising: a plurality of fine particles formed of the brittle materialby pre-treating raw brittle material particles in at least one of a ballmill, a vibrating mill and a planetary grinder so as to increase aninternal strain thereof while limiting formation of cracks therein. 10.A material for forming composite structure according to claim 9, whereinthe fine particles are adapted to be incorporated into an aerosol sothat a mechanical impact can be imparted thereto by blowing the aerosolagainst the substrate; and the particles generate an active new surfaceupon collision with the substrate surface after fractured due to themechanical impact.
 11. A material for forming composite structureaccording to claim 9, wherein the internal strain of the fine particlesis 0.25%˜2.0%.
 12. A material for forming composite structure accordingto claim 9, wherein an average size of the fine particles is 0.1˜5 μm.13. A material for forming composite structure according to claim 11,wherein an average size of the fine particles is 0.1˜5 μm.